Simplify the following expression: $\dfrac{18p^4}{21p^5}$ You can assume $p \neq 0$.
Explanation: $ \dfrac{18p^4}{21p^5} = \dfrac{18}{21} \cdot \dfrac{p^4}{p^5} $ To simplify $\frac{18}{21}$ , find the greatest common factor (GCD) of $18$ and $21$ $18 = 2 \cdot 3 \cdot 3$ $21 = 3 \cdot 7$ $ \mbox{GCD}(18, 21) = 3 $ $ \dfrac{18}{21} \cdot \dfrac{p^4}{p^5} = \dfrac{3 \cdot 6}{3 \cdot 7} \cdot \dfrac{p^4}{p^5} $ $\phantom{ \dfrac{18}{21} \cdot \dfrac{4}{5}} = \dfrac{6}{7} \cdot \dfrac{p^4}{p^5} $ $ \dfrac{p^4}{p^5} = \dfrac{p \cdot p \cdot p \cdot p}{p \cdot p \cdot p \cdot p \cdot p} = \dfrac{1}{p} $ $ \dfrac{6}{7} \cdot \dfrac{1}{p} = \dfrac{6}{7p} $